In the conventional color electrostatic recording apparatus, for example, in Nippon Steel's "A0-size single pass color electrostatic plotter X2020", as shown in FIG. 1, the recording paper wound on a drum 10 is drawn out and fed by a feeder roller 20 at a given speed, and passes through four primary color recording sections for black, cyan, magenta, and yellow. When passing each primary color recording section, an image of the corresponding color component is recorded on the recording paper. More particularly, as shown in FIG. 2, as the recording paper 1 passes each primary color recording section, the electrostatic latent image of the image of the respective color component is recorded on the recording side of the recording paper 1 by the electrostatic recording head 2. At a liquid development unit 4, a liquid toner of the respective color is carried with spiral grooves (not shown) formed in the surface of a rotating toner roll 4a, and applied to the recording side of the recording paper 1. Since the liquid toner is charged in a polarity opposite to the polarity of the charge on the electrostatic latent image, the toner adheres to the portions of the recording paper where the latent image is formed. The recording paper 1 is moved further, and an excess toner is removed by the toner vacuum channel 5, and the recording paper is dried by the drying device.
The drying device includes a plurality of air blowers 56, and a dry air supplied from the air blowers 56 passes through a passage 54, and is blown against the rear surface of the recording paper 1. The dry air blown against the recording paper 1 is exhausted through an opening 60 formed between an upper end of a side wall 58 and the recording paper 1 to the outside or exhaust chamber 62. The liquid toner is mainly dried by the dry air in contact with the recording paper 1 when the dry air passes near the opening 60. However, since the volume and the direction of the air passing through the opening are not uniform in the width-wise direction of the recording paper 1, there occur turbulence or stagnation in the drying air so that the unevenness occurs in the drying of the liquid toner, which results in the unevenness of the image recorded on the recording paper 1. It is considered that this is because the drying air is blown against the recording paper and immediately diffused. Pressure rolls 4b are provided to prevent the recording paper 1 from being raised by the dry air and separated from the toner vacuum channel 5, and thereby to keep the paper in close contact with the toner roll 4a and the vacuum channel 5.
FIG. 3 shows an example of the uneven quality of the image recorded on the recording paper 1. This example shows the insufficiently dried portions 51 in the width-wise direction of the recording paper 1, namely, both edges of the paper and the other portions corresponding to the top of each of the blowers and the intermediate spaces between adjacent two blowers. The toner is generally fixed on the paper as dried. However, if the wet or insufficiently dried portion exists, the toner fixed on the wet portion is resolved at the following developer and also the wet portion may cause insufficient discharge for recording the latent image for different color by the head of the following developer. Sometimes, the toner fixed on the wet portion is scraped and fixed on the head surface and piled up thereon causing shortage of electrodes of the head, resulting in damage of the head.
In this prior art example, the recording paper width is 914 mm, the transport speed 12.7 mm/sec, the air flow rate 5 m.sup.3 /min, the width of the passage 54 (distance in the moving direction of the recording paper) 20 mm, and the width of the opening 60 (the distance between the upper end of the side wall 58 and the recording paper 1) 50 mm.
Another problem with the drying device of the conventional electrostatic recording apparatus using a liquid toner is in the recovery of the organic solvent used in the liquid toner. Since a liquid toner has toner particles dispersed in a liquid organic solvent, the recording paper is wetted by the solvent. Generally, in the current apparatus of the liquid development system, an excess solvent is recovered, but because of drying with dry air that follows, part of the organic solvent is discharged together with the exhaust gas. As it is not desirable from an environmental point of view that the solvent is diffused in the air, the development of a recovery system has been studied which recovers the solvent from the apparatus while increasing air-tightness, and providing a limited outlet to the outside. Recently, the trend has been toward adoption of recovery system of this type, particularly with small-size printers.
However, with the apparatus of a type using dry air blowing, it is difficult to satisfactorily recover a solvent such as Isopar contained in the exhaust air and it is feared that this type of apparatus has adverse affects on the environment.